Spacer device and insertion instrument for use in anterior cervical fixation surgery

ABSTRACT

An intervertebral spacer has curvate upper and lower rough surfaces that stimulate bone growth and is formed from a porous material that facilitates bone growth thereinto. The spacer has a plurality of smooth linear grooves to facilitate insertion of the spacer into an intervertebral space using a spacer insertion tool that has a scissor-style body. Each of the insertion tool&#39;s arm&#39;s heads has an inner surface having a pair of smoothed linear protrusions that fit within the linear grooves of the spacer when the heads are closed about the spacer. When the spacer is held, spaces are present between the spacer&#39;s rough surfaces and the heads&#39; inner surfaces so that when the protrusions are longitudinally slid from the grooves to leave the spacer in the intervertebral spacer, the rough surfaces are not disturbed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/715,965, filed on Nov. 18, 2003 which is a continuation of U.S.application Ser. No. 10/001,531, filed on Nov. 30, 2001, the disclosuresof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to a medical instrument for use inanterior cervical spine surgery and more specifically to a spacer deviceand insertion instrument used in the treatment and correction ofpathologies in the cervical spine.

The spinal column consists of more than 20 discrete bones which arejoined together in a highly complex arrangement which houses andprotects critical elements of the nervous system and serves as astructural framework around which there are innumerable peripheralnerves and circulatory bodies in close proximity. In spite of thesecomplicating features, the spine is a highly flexible structure, capableof a high degree of curvature and twist in nearly every directionpermitting human beings a high degree of physical dexterity. In generalthese bones are coupled sequentially to one another by tri-jointcomplexes which consists of an anterior intervertebral disc and the twoposterior facet joints. The anterior intervertebral discs of adjacentbones are cushioning cartilage spacers.

The bones and connective tissue of the neck, or cervical spine, areparticularly complex in that they are smaller, are the most flexible inthe spinal column, and are adjacent to the most critical circulatory,respiratory, and digestive tissues in the body. Long term degenerationof the cartilage spacers and/or trauma, can cause adjacent bones of thecervical spine to collapse together and/or become axially displaced(that is, become segmentally offset). These and other failure modes cancause significant pain as well as catastrophic neurological problems.

The traditional course of surgical treatment can include theimplantation of a plate which seats against the anterior surfaces ofadjacent bones, and the fixation of the plate thereto with bone screwsimmobilizes the two bones in the distracted and aligned position.

Concerns for the overall safety of this method of treatment, however,include the risk of screw pull out and/or breakage, or plate breakage,each of which are accompanied by the severe risk of esophegealperforation, which can be fatal if not treated immediately andaggressively. The surgical effectiveness of this treatment is enhanceddramatically if the adjacent bones are able to fuse together across thedistracted space, thus forming a single bony element which can supportthe neck without needing to load the metal plate (thus risking breakageor other failure mode). The problem is that the distraction increasesthe distance between the fusing bones, and the need to create the bonebridge requires that the bones be close enough to grow together. Thesecompeting factors have made the use of porous material as a spacermaterial desirable. This spacer physically braces the bones at thedesired positions, permitting the bones to fuse across the entireassembly.

Similar techniques have been employed in other spinal infirmities,including collapsed disc spaces in the thoraco-lumbar regions of thespine. The present invention is therefore applicable to the treatment ofany spinal disorder in which the space between vertebral bones needs tobe surgically separated (the bones distracted), and then fused to oneanother, however, for the purposes of this invention disclosure, onlythe application to the cervical spine shall be described hereinbelow.

Before the implant may be inserted into the space, however, the heightof the disc space (the distance between the opposing end plates of theadjacent bones) must be restored. Restoring the appropriate height andorientation of the vertebral bones and the intervertebral space iscritical, and when done properly (that is, through a series ofsequentially larger trial spacers) is also instructive for the purposesof determining the appropriate size of the implant to be provided.

It shall be understood that the use of an anterior cervical plate inconjunction with the foregoing will be the preferred method of surgicaltreatment, however, its use should not be considered a requirement inthe practice of the present invention, which should be viewed as awholly separate and independent surgical process.

It is, therefore, an object of the present invention to provide a newand novel treatment for cervical disc pathology, as well as for thetreatment of spinal pathologies in general.

It is, correspondingly, another object of the present invention toprovide an intervertebral distraction tool that more accurately andeasily separates collapsed intervertebral spaces and restores the properanatomical orientation of cervical bones.

It is further an object of the present invention to provide animplantable intervertebral spacer device, and insertion instrument,which permits more anatomically appropriate and rapidly osteogenicfusion across the intervertebral space.

Other objects of the present invention not explicitly stated will be setforth and will be more clearly understood in conjunction with thedescriptions of the preferred embodiments disclosed hereafter.

BRIEF SUMMARY OF THE INVENTION

The preceding objects of the invention are achieved by the presentinvention, which provides an intervertebral distraction tool and anintervertebral spacer device and insertion instrument.

A preferred embodiment of an intervertebral distraction tool (alsoreferred to herein as a trial) of the present invention has a proximalend defined by an elongate shaft, and a distal end defined by aclamshell head. The head has upper and lower halves, each having acurvate outer surface and a flat inner surface. The distal side of thehead is hinged so that the head opens and closes from the proximal sideof the head. Preferably, the hinge is a separating hinge that allows thehalves to not only angulate with respect to one another about the hingeaxis, but also to vertically separate from one another at the hinge.Preferably, the proximal side of the head has a tapered lip thatfacilitates insertion of the distal end of the distraction separator(described below) in between the halves. The head further has a pair ofposts and corresponding bores into which the posts compress fit when thehead is closed. The force of the compression fit holds the head closed,so that the head can be held closed during the insertion of the headinto the target intervertebral space. When the distraction separator isactuated to open the head, the compression force is overcome to allowthe head to open.

A preferred embodiment of a distraction separator of the presentinvention has an elongate shaft having a longitudinal bore. The distalend of the shaft has a decreasing taper defined by upper and lowersurfaces that are angled toward one another, terminating at a distalface of the separator. The longitudinal bore accommodates the elongateshaft of the trial so that the separator can be moved longitudinallyrelative to the shaft. The longitudinal movement is preferably effectedby simply pushing the proximal end of the separator toward the head ofthe trial. Upon forward movement of the separator, the tapered upper andlower surfaces engage the flat inner surfaces of the head, causing thehalves to angulate about the hinge axis of the head, thereby opening thehead. Further advancement of the separator in between the halves causesthe halves to not only angulate with respect to one another about thehinge axis, but also to vertically separate from one another at thehinge, due to the separating hinge. Once the head has been opened asdesired by the surgeon, extraction of the separator from between thehalves and removal of the head from the intervertebral space leaves thedistracted space ready for accepting additional trials or for insertionof a spacer of the present invention.

A preferred embodiment of a spacer device of the present invention has athickness that is preferably predetermined to be a distance that is tobe established between two vertebral discs that are to be fusedtogether. The spacer further has an overall rectangular shape withrounded corners to limit interference with surrounding tissue during theinsertion procedure. The spacer further has upper and lower surfacesthat are curvate to allow them to more easily fit into and remain in theintervertebral space, with each curvate surface seating within thevertebral cavity presented to the surface when the spacer is disposed inthe intervertebral space. The spacer is preferably formed from amaterial that can withstand compressive forces that are present withinan intervertebral space, and further is preferably formed of a porousmaterial that facilitates bone growth thereinto for a successful fusionprocedure. Further preferably, the upper and lower surfaces are roughsurfaces that will stimulate bone growth into the porous material. Thespacer further has a plurality of linear grooves to facilitate insertionof the spacer into the intervertebral space. Each of the grooves has adepth, preferably is rounded, and preferably has a smooth surface.

A preferred embodiment of a spacer insertion tool of the presentinvention has a scissor-style body having upper and lower arms hingedabout a hinge rod, each of the arms having a distal end having a head,each of the arms having a proximal end having a gripping handle. Each ofthe heads has an inner surface having a pair of linear protrusions thatare spaced and dimensioned to fit within the linear grooves of thespacer when the heads are closed about the spacer. That is, when thearms are actuated by a surgeon gripping and bringing together thehandles, the arms hinge about the hinge rod and therefore the heads arebrought to bear on the spacer such that each of the protrusions fitsinto a respective one of the grooves, and the spacer is held between theheads by the continual compression of the spacer in this manner.Accordingly, the surgeon, while holding the spacer with the arms, caninsert the spacer into the intervertebral space that has beendistracted.

It should be noted that when the spacer is held with the arms, the upperand lower curvate surfaces are preferably not engaged by the heads. Thatis, the dimensions of the protrusions and/or the grooves are such thatspaces are present between the upper and lower curvate surfaces and theinner surfaces of the heads. This feature is primarily provided so thatwhen the spacer is released from the insertion tool, the upper and lowersurfaces are not altered during the removal of the heads from thespacer.

In order to facilitate removal of the heads from the spacer so that thespacer can be left in the intervertebral space, the insertion tool isconfigured such that the arms can be moved longitudinally relative to abracing rod. In the illustrated embodiment, this feature is providedinasmuch as the insertion tool is provided with a bore, preferablythough the hinge rod, and the bracing rod is disposed through the bore.

In operation to remove the heads from the spacer while holding thespacer in the intervertebral space, the distal end of the bracing rod isheld against the spacer by the surgeon while the surgeon pulls thehandles. The pulling of the handles while the spacer is held in theintervertebral space causes the protrusions to slide out of the groovesuntil the spacer is released from the heads and is compressed betweenthe vertebral discs by the natural compression force present in thespine. Accordingly, the upper and lower surfaces of the spacer, beingcurvate, easily fit into and remain in the intervertebral space, witheach curvate surface seating within the vertebral cavity presented tothe surface when the spacer is disposed in the intervertebral space.Further, the surfaces being rough, stimulate bone growth, and beingporous, provide for bone growth into the material to facilitate fusion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-c show an intervertebral distraction tool in two side views(FIG. 1 a where the trial is closed, and FIG. 1 b where the trial isopen) and a top view, respectively.

FIGS. 2 a-c show a distraction separator of the present invention inside, top and side views, respectively (with FIG. 2 c showing theseparator advanced within the trial of FIGS. 1 a-c).

FIGS. 3 a-c show a spacer device of the present invention in side, frontand top views, respectively.

FIGS. 4 a-b show a spacer insertion tool of the present invention in aside view and a front view, respectively, each showing the insertiontool holding the spacer of FIGS. 3 a-c of the present invention, and thefront view omitting the arms and handles of the insertion tool.

DETAILED DESCRIPTION

While the present invention will be described more fully hereinafterwith reference to the accompanying drawings, in which particularembodiments and methods of implantation are shown, it is to beunderstood at the outset that persons skilled in the art may modify theinvention herein described while achieving the functions and results ofthis invention. Accordingly, the descriptions that follow are to beunderstood as illustrative and exemplary of specific structures, aspectsand features within the broad scope of the present invention and not aslimiting of such broad scope. Like numbers refer to similar features oflike elements throughout.

Referring now to FIGS. 1 a-c, an intervertebral distraction tool 100 isshown in two side views (FIG. 1 a where the trial 100 is closed, andFIG. 1 b where the trial 100 is open) and a top view, respectively. Thetrial 100 has a proximal end 132 and a distal end 134, the proximal end132 being defined by an elongate shaft 136, and the distal end 134 beingdefined by a clamshell head 138. The head 138 has an overall rectangularshape with rounded corners to limit interference with surrounding tissueduring the distraction procedure. It should be understood that the shapeof the head 138 can be any shape that fits between vertebral bodies,that other embodiments of the present invention may not use rectangularshaped heads. Further, other embodiments of the present invention may ormay not have rounded corners on the head 138, depending on the clinicalnecessity or desirability of such or similar features.

The head 138 has upper 102 and lower 104 halves, each having a curvateouter surface 106, 108 and a flat inner surface 110, 112. As will bedescribed below, the curvature of the outer surfaces 106, 108facilitates the distraction of the vertebral bodies, but it should beunderstood that the curvature is not necessary for the functioning ofthe present invention, and that outer surfaces of alternate conformitycan be used without departing from the scope of the present invention.Similarly, the flat contour of the inner surfaces 110, 112 is preferred,but other contours can be provided within the scope of the presentinvention.

The distal side 140 of the head 138 is hinged so that the head 138 opensand closes from the proximal side 142 of the head 138. Preferably, asshown, the hinge 114 is a separating hinge that allows the halves 102,104 to not only angulate with respect to one another about the hingeaxis, but also to vertically separate from one another at the hinge.This is achieved by the use of a hinge pin 116 having a diameter smallerthan the height of the each half's hinge bore 118, 120. It should beunderstood that the use of a separating hinge is not necessary for thefunctioning of the present invention, but rather is preferred, and thatnonseparating hinges, and other mechanisms that allow the halves toangulate with respect to one another (with or without separatingvertically) can be provided within the scope of the present invention.

Preferably, as shown, the proximal side 142 of the head 138 has atapered lip 122 that facilitates insertion of the distal end of thedistraction separator (described below) in between the halves 102, 104(best shown in FIG. 2 c, described below). The head 138 further has apair of posts 124, 126 and corresponding bores 128, 130 into which theposts 124, 126 compress fit when the head 138 is closed. The force ofthe compression fit holds the head 138 closed, so that the head 138 canbe held closed during the insertion of the head 138 into the targetintervertebral space (the space into which the spacer of the presentinvention, described below, will be placed to facilitate fusion of theadjacent vertebral bodies). When the distraction separator (describedbelow) is actuated to open the head 138, the compression force isovercome to allow the head 138 to open. It should be understood that thepost and bore configuration is preferable, but that other mechanisms canbe provided to hold the head 138 closed, without departing from thescope of the present invention.

Referring now to FIGS. 2 a-c, a distraction separator 200 of the presentinvention is shown in side, top and side views, respectively (with FIG.2 c showing the separator 200 advanced within the trial 100 describedabove). The separator 200 has an elongate shaft 202 having alongitudinal bore 208 and a proximal end 204 and a distal end 206. Thedistal end 206 has a decreasing taper defined by upper 210 and lower 212surfaces that are angled toward one another, terminating at a distalface 214 of the separator 200. The longitudinal bore 208 accommodatesthe elongate shaft 136 of the trial 100 so that the separator 200 can bemoved longitudinally relative to the shaft 136. The longitudinalmovement is preferably effected by simply pushing the proximal end 204toward the head 138. However, it should be noted that other mechanismsfor moving the separator 200 can be used, including, but not limited to,for example, providing threads on the walls of the longitudinal bore208, corresponding threads on the outer surface of the shaft 136, andproviding for rotational movement of the threaded portions of the shaft136 relative to the distal end 134 of the shaft 136, so that rotation ofthe shaft 136 causes forward movement of the separator 200 relative tothe shaft 136 and reverse rotation of the shaft 136 causes backwardmovement of the separator 200 relative to the shaft 136.

As best shown in FIG. 2 c, upon forward movement of the separator 200,the tapered upper and lower surfaces 210, 212 engage the flat innersurfaces 110, 112 of the head 138, causing the halves 102,104 toangulate about the hinge axis of the head 138, thereby opening the head138. The further the separator 200 is advanced in between the halves102, 104, the further the head 138 opens. Therefore, the surgeon canvary the amount of distraction. In addition, further advancement of theseparator 200 in between the halves 102, 104 causes the halves 102,104to not only angulate with respect to one another about the hinge axis,but also to vertically separate from one another at the hinge, due tothe separating hinge 114. Once the head 138 has been opened as desiredby the surgeon, extraction of the separator 200 from between the halves102,104 (preferably by simply pulling on the proximal end 204, butalternatively by other mechanisms, as described above) and removal ofthe head 138 from the intervertebral space leaves the distracted spaceready for accepting additional trials (for example, thicker trialsand/or trials that open to greater distances) or for insertion of aspacer of the present invention (described below). With regard toaccepting additional trials, it should be noted that a plurality oftrials can be provided, each having an individually unique thicknessand/or an individually unique distance to which the head of the trialcan be opened. Therefore, the surgeon can distract the space to anydesired distance through the use of one or more of such trials.

With regard to inserting spacers, and referring now to FIGS. 3 a-c, aspacer 300 of the present invention is shown in side, front and topviews, respectively. The spacer 300 has a thickness 302 that ispreferably predetermined to be a distance that is to be establishedbetween two vertebral discs that are to be fused together. The spacer300 further has an overall rectangular shape with rounded corners andedges to limit interference with surrounding tissue during the insertionprocedure. It should be understood that the shape of the spacer 300 canbe any shape that fits between vertebral bodies, that other embodimentsof the present invention may not use rectangular shaped heads. Further,other embodiments of the present invention may or may not have roundedcorners or edges on the spacer 300, depending on the clinical necessityor desirability of such or similar features.

The spacer 300 further has upper and lower surfaces 304, 306 that arecurvate to allow them to more easily fit into and remain in theintervertebral space, with each curvate surface 304, 306 seating withinthe vertebral cavity presented to the surface when the spacer 300 isdisposed in the intervertebral space. These surfaces give the spacer 300a shape similar to a pillow. It should be understood that the curvatureis preferable but not necessary for the functioning of the presentinvention, and that surfaces of alternate conformity can be used withoutdeparting from the scope of the present invention.

The spacer 300 is preferably formed from a material that can withstandcompressive forces that are present within an intervertebral space, andfurther is preferably formed of a porous material that facilitates bonegrowth thereinto for a successful fusion procedure. Examples ofmaterials suitable for this purpose include porous metals and compactedwire meshes, bone morphogenic protein, and polylactic lactic acid.Further preferably, the upper and lower surfaces 304, 306 are roughsurfaces that will stimulate bone growth into the porous material.

The spacer 300 further has a plurality of linear grooves 308, 309, 310,311 to facilitate insertion of the spacer 300 into the intervertebralspace (as described below). For reasons explained in greater detailbelow, each of the grooves has a depth 312, preferably is rounded, andpreferably has a smooth surface. It should be noted that although twogrooves are shown on each upper and lower surface of the spacer, more orfewer grooves can be used without departing from the scope of thepresent invention.

It should be understood that a plurality of spacers 300 of the presentinvention can be provided, having individually unique thicknesses.Preferably, the thicknesses are predetermined to be distances that areto be established between two vertebral discs that are to be fusedtogether. That is, depending on the clinical application, theintervertebral space may be distracted to a particular distance (e.g.,by the distraction process described above), and a plurality of spacerscan be provided with different thicknesses so that at least one has athickness matching the particular intervertebral distance in any givenclinical application. Preferably, each of the plurality of spacers haslinear grooves that preferably are of the same depth 312 from spacer tospacer (so that if desired a single insertion tool (e.g., of a typedescribed below) can be used to insert more than one of the spacers),preferably are rounded, and preferably have smooth surfaces.

Referring now to FIGS. 4 a-b, a spacer insertion tool 400 of the presentinvention is shown in a side view and a front view, respectively, eachshowing the insertion tool 400 holding the spacer 300 of the presentinvention, and the front view omitting the arms and handles of theinsertion tool. The insertion tool 400 has a scissor-style body 402having upper 404 and lower 406 arms hinged about a hinge rod 408, eachof the arms 404, 406 having a distal end 410, 412 having a head 414,416, each of the arms 404, 406 having a proximal end 418, 420 having agripping handle 422, 424. It should be noted that while the insertiontool 400 of the illustrated embodiment has a scissor-style body 402 toopen and close the heads 414, 416, other embodiments of the presentinvention may have bodies of other styles that may or may not utilizehinges or similar structures to open and close the heads 414, 416.

Each of the heads 414, 416 has an inner surface 426, 428 having a pairof linear protrusions 430, 432, 434, 436 that are spaced and dimensionedto fit within the linear grooves 308, 309, 310, 311 of the spacer 300when the heads 414, 416 are closed about the spacer 300. (As notedabove, although two grooves are shown on each upper and lower surface ofthe spacer, more or fewer grooves can be used without departing from thescope of the present invention, and hence more or fewer correspondingprotrusions can be used on the heads 414, 416 without departing from thescope of the present invention; it should also be noted that it is notnecessary for the number of grooves to equal the number of protrusions.)That is, when the arms 404, 406 are actuated by a surgeon gripping andbringing together the handles 422, 424, the arms 404,406 hinge about thehinge rod 408 and therefore the heads 414, 416 are brought to bear onthe spacer 300 such that each of the protrusions 430, 432, 434, 436 fitsinto a respective one of the grooves 308, 309, 310, 311, and the spacer300 is held between the heads 414, 416 by the continual compression ofthe spacer 300 in this manner. Accordingly, the surgeon, while holdingthe spacer 300 with the arms 404, 406, can insert the spacer 300 intothe intervertebral space that has been distracted (e.g., according tothe procedures described above).

It should be noted that when the spacer 300 is held with the arms 404,406, the upper and lower curvate surfaces 304, 306 are preferably notengaged by the heads 414, 416. That is, the dimensions of theprotrusions 430, 432, 434, 436 and/or the grooves 308, 309, 310, 311 aresuch that spaces 438, 440 are present between the upper and lowercurvate surfaces 304, 306 and the inner surfaces 426, 428 of the heads414, 416. This feature is primarily provided so that when the spacer 300is released from the insertion tool 400 (as described below), the upperand lower surfaces 304, 306 (preferably being rough and porous as notedabove) are not altered during the removal of the heads 414, 416 from thespacer 300. During the removal, the heads 414, 416 only engage thespacer 300 at the grooves 308, 309, 310, 311, and therefore the upperand lower surfaces 304, 306 are not at risk for being damaged.

In order to facilitate removal of the heads 414, 416 from the spacer 300so that the spacer 300 can be left in the intervertebral space, theinsertion tool 400 is configured such that the arms 404, 406 can bemoved longitudinally relative to a bracing rod 444. In the illustratedembodiment, this feature is provided inasmuch as the insertion tool isprovided with a bore 442, preferably though the hinge rod 408 as shown,and the bracing rod 444 that is disposed through the bore 442. It shouldbe understood that other embodiments may use other configurations toeffect the same or similar functionality.

The longitudinal movement of the arms 404,406 relative to the bracingrod 444 is preferably effected by holding the bracing rod 444 andpulling the handles 422, 424. The bracing rod 444 has a proximal end 446and a distal end 448. In operation to remove the heads 414, 416 from thespacer 300 while holding the spacer 300 in the intervertebral space, thedistal end 448 of the bracing rod 444 is held against the spacer 300 bythe surgeon (e.g., by gripping and maintaining the position of theproximal end) while the surgeon pulls the handles 422, 424. The pullingof the handles 422, 424 while the spacer 300 is held in theintervertebral space causes the protrusions 430, 432, 424, 436 to slideout of the grooves 308, 309, 310, 311 (the grooves and the protrusionsare preferably rounded and smoothed as noted above to facilitate thissliding) until the spacer 300 is released from the heads 414, 416 and iscompressed between the vertebral discs by the natural compression forcepresent in the spine. Accordingly, the upper and lower surfaces 304, 306of the spacer 300, being curvate, easily fit into and remain in theintervertebral space, with each curvate surface 304, 306 seating withinthe vertebral cavity presented to the surface when the spacer 300 isdisposed in the intervertebral space. Further, the surfaces 304, 306being rough, stimulate bone growth, and being porous, provide for bonegrowth into the material to facilitate fusion.

It should be noted that other mechanisms for moving the arms 404, 406relative to the bracing rod 444 can be used, including, but not limitedto, for example, providing threads on the walls of the bore 442,corresponding threads on the outer surface of the bracing rod 444, andproviding for rotational movement of the threaded portion of the bracingrod 444 relative to the distal end 448 of the bracing rod 444, so thatrotation of the bracing rod 444 causes forward movement of the arms 404,406 relative to the bracing rod 444 and reverse rotation of the bracingrod 444 causes backward movement of the arms 404, 406 relative to thebracing rod 444.

It should also be noted that if desired, a plurality of insertion tools400 can be provided for inserting a plurality of spacers 300, where thespacers 300 are of different thicknesses and the insertion tools 400open to different distances, so that one or more insertion tools 400 canbe used to more effectively grip a particular spacer or set of spacers300.

While there has been described and illustrated specific embodiments ofthe present invention, it will be apparent to those skilled in the artthat variations and modifications are possible without deviating fromthe broad spirit and principle of the present invention. The invention,therefore, shall not be limited to the specific embodiments discussedherein.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. An assembly, comprising: an intervertebral spacer dimensioned to fitbetween two vertebrae, the intervertebral spacer having a spacer bodyhaving a leading end, a trailing end, and first and second sidesextending between the leading and trailing ends, the spacer body havingan upper surface with a first linear groove and a lower surface with asecond linear groove, the first and second linear grooves extending in afirst direction, the upper and lower surfaces being convexly curvedalong a plane extending between the leading and trailing ends and alonga plane extending between the first and second sides; and an insertiontool for inserting the intervertebral spacer into an intervertebralspace, the insertion tool including: an upper arm having a first linearprotrusion, the first linear protrusion placed within the first lineargroove; a lower arm having a second linear protrusion, the second linearprotrusion placed within the second linear groove; a hinge rod hingeablycoupling the upper and lower arms; and a bracing rod extending throughthe hinge rod and in contact with the intervertebral spacer, wherein theupper and lower arms can be moved in the first direction with respect tothe bracing rod and intervertebral spacer.
 2. The assembly of claim 1,wherein the upper arm includes a first head with the first linearprotrusion extending therefrom and the lower arm includes a second headwith the second linear protrusion extending therefrom, the first andsecond head located a distal end of the insertion tool.
 3. The assemblyof claim 2, wherein the upper arm includes a first gripping handle andthe lower arm includes a second gripping handle, the first and secondgripping handles located a proximal end of the insertion tool.
 4. Theassebmly of claim 3, wherein movement of the first and second grippinghandles towards one another causes movement of the first and secondheads towards one another.
 5. The assembly of claim 2, wherein when thefirst linear protrusion is placed within the first linear groove and thesecond linear protrusion is placed within the second linear groove, thefirst head is spaced from the upper surface and the second head isspaced from the lower surface.
 6. The assembly of claim 1, wherein thefirst and second linear grooves and the first and second linearprotrusions are parallel.
 7. The assembly of claim 1, wherein theintervertebral spacer has a rectangular pillow shape.
 8. The assembly ofclaim 1, wherein the intervertebral spacer is formed of a porousmaterial.
 9. The assembly of claim 8, wherein the porous material of thespacer body is selected from the group consisting of porous metals,compacted wire meshes, bone morphogenic protein, and polylactic acid.10. The assembly of claim 2, wherein two first linear protrusions of thefirst head are placed within two first linear grooves of the uppersurface, and two second linear protrusion of the second head are placedwithin two second linear grooves of the lower surface.
 11. The assemblyof claim 10, wherein when the two first linear protrusions are placedwithin the two first linear grooves and the two second linearprotrusions are placed within the two second linear grooves, the firsthead is spaced from the upper surface and the second head is spaced fromthe lower surface.
 12. The assembly of claim 2, wherein each lineargroove in the two first linear grooves is directly opposite a respectiveone of the two second linear grooves.
 13. The assembly of claim 1,wherein the hinge rod includes a bore for slidably accepting the bracingrod.
 14. An assembly, comprising: an intervertebral spacer dimensionedto fit between two vertebrae, the intervertebral spacer having a spacerbody having a leading end, a trailing end, and first and second sidesextending between the leading and trailing ends, the spacer body havingan upper surface with a first linear groove and a lower surface with asecond linear groove, the first and second linear grooves extending in afirst direction, and the upper and lower surfaces being convexly curvedalong a plane extending between the first and second sides; and aninsertion tool for inserting the intervertebral spacer into anintervertebral space, the insertion tool including: an upper arm havinga first head with a first linear protrusion, the first linear protrusionplaced within the first linear groove; a lower arm having a second headwith a second linear protrusion, the second linear protrusion placedwithin the second linear groove; and a hinge rod hingeably coupling theupper and lower arms, wherein when the first linear protrusion is placedwithin the first linear groove and the second linear protrusion isplaced within the second linear groove, the first head is spaced fromthe upper surface and the second head is spaced from the lower surface.15. The assembly of claim 14, further comprising a bracing rod extendingthrough the hinge rod and in contact with the intervertebral spacer, sothat the upper and lower arms can be moved in the first direction withrespect to the bracing rod and intervertebral spacer.
 16. The assemblyof claim 14, wherein the upper arm includes a first gripping handle andthe lower arm includes a second gripping handle, the first and secondgripping handles located a proximal end of the insertion tool.
 17. Theassebmly of claim 16, wherein movement of the first and second grippinghandles towards one another causes movement of the first and secondheads towards one another.
 18. The assembly of claim 14, wherein thefirst and second linear grooves and the first and second linearprotrusions are parallel.
 19. The assembly of claim 14, wherein theintervertebral spacer has a rectangular pillow shape.
 20. The assemblyof claim 14, wherein the intervertebral spacer is formed of a porousmaterial.
 21. The assembly of claim 20, wherein the porous material ofthe spacer body is selected from the group consisting of porous metals,compacted wire meshes, bone morphogenic protein, and polylactic acid.22. The assembly of claim 14, wherein two first linear protrusions ofthe first head are placed within two first linear grooves of the uppersurface, and two second linear protrusion of the second head are placedwithin two second linear grooves of the lower surface.
 23. The assemblyof claim 22, wherein each linear groove in the two first linear groovesis directly opposite a respective one of the two second linear grooves.24. The assembly of claim 15, wherein the hinge rod includes a bore forslidably accepting the bracing rod.
 25. An assembly, comprising: anintervertebral spacer dimensioned to fit between two vertebrae, theintervertebral spacer having a spacer body having a leading end, atrailing end, and first and second sides extending between the leadingand trailing ends, the spacer body having an upper surface with twofirst linear grooves and a lower surface with two second linear grooves,the first and second linear grooves extending in a first direction, andthe upper and lower surfaces being convexly curved along a planeextending between the leading and trailing ends and along a planeextending between the first and second sides; and an insertion tool forinserting the intervertebral spacer into an intervertebral space, theinsertion tool including: an upper arm having a first head with twofirst linear protrusions, the two first linear protrusions placed withinthe two first linear groove, the first head being spaced from the uppersurface; a lower arm having a second head with two second linearprotrusions, the two second linear protrusions placed within the twosecond linear grooves, the second head being spaced from the lowersurface; a hinge rod hingeably coupling the upper and lower arms, thehinge rod having a bore formed therethrough; and a bracing rod extendingthrough the hinge rod bore and in contact with the intervertebralspacer, wherein the upper and lower arms can be moved in the firstdirection with respect to the bracing rod and intervertebral spacer.